High-temperature phase relationships for YxNd1-xBa2Cu3O (0 <= x <= 0.5) superconductors via containerless processing

This paper presents the results of drop-tube experiments performed on YxNd1 -xBa2Cu3Oy (0 less than or equal to x less than or equal to 0.5) to underst and some of the effects of partial substitutions of Nd for Y on the phase r elationships in these systems at elevated temperatures. Powders from 50 to 100 mu m in diameter were processed in pure O-2 at furnace temperatures fro m 1400 to 1800 degrees C, every 25 degrees C, The resulting samples were ex amined microstructurally using scanning electron microscopy, energy dispers ive spectroscopy, and optical microscopy. Powder x-ray diffraction was perf ormed for phase identification. It was verified that Nd substitution alters phase selection by introducing at least one new phase and allowing for sol idification of the superconducting composition directly from the melt via u ndercooling to below the peritectic transformation temperature. In addition , solidification pathways are altered for samples processed at temperatures just below the liquidus temperature. Microstructural and x-ray diffraction evidence was used to map the liquidus with increasing Nd substitution. It was found that a minimum in this liquidus occurs at or near the composition Y0.1Nd0.9Ba2Cu3Ox and at a temperature of 1500 degrees C (+/-25 degrees C) .